Light brahma rooster or hen?

Some friends gave us one of their light brahma chickens that they said was a rooster. Now I'm starting to think he is really a pullet. He doesn't look like a rooster to me, but I just can't decide. I don't have any other brahmas to compare him to. Our friends are new to chicken keeping so I wonder if they made a mistake. He's almost 18 weeks old. Thoughts? Thanks!